On the M100s I have found most of the caps tend to leak (and cause PCB damage). While I am NOT a proponent of 'recapping' every piece of vintage gear out there on the M100 I do a full recap on every one of them.
The -5V also goes to the RS-232 circuitry so if something is amiss there it can load down the supply. My best guess though is that if you replace the rest of the electrolytics on the board and clean up any damage caused by the leaking ones that will solve the issue. I have had a few odd power supply related issues caused by invisible conductive gunk on the top side of the PCB and/or the flux they applied to the bottom of the PCB with a butter knife, turning conductive. Jeff Birt -----Original Message----- From: M100 <[email protected]> On Behalf Of Eric LK Sent: Sunday, March 21, 2021 2:05 AM To: [email protected] Subject: [M100] Need help fixing VEE on M100 About 6 months ago, my M100's LCD contrast was very weak and impossible to use. Following your advice, I changed C82 and C85 . That gave me a solid -5V for VEE and the contrast was back to normal. My problem is that 6 months later, I can still read the screen (mostly) but my VEE is now back to -3V. I'm tempted to replace C82 and C85 again, but I think it's weird to get the same failure so quickly after a fix (both new capacitors were new from mouser). Do you see anything else I should check regarding this issue? Eric
